The present disclosure relates to a switch device that includes a chalcogenide layer between electrodes and to a storage unit that includes the switch device.
Recently, it has been demanded to increase capacity of a non-volatile memory for data storage which is typified by a resistance-variation-type memory such as a ReRAM (Resistance Random Access Memory) and a PRAM (Phase-change Random Access Memory). However, in a resistance-variation-type memory using a currently-available access transistor, the floor area per unit cell is large. For this reason, for example, when compared to a flash memory such as that of a NAND type, it has been difficult to increase capacity even the memory is miniaturized based on the same design rule. In contrast, when a so-called cross point array structure in which memory devices are arranged at intersections (cross points) of intersecting wirings is adopted, the floor area per unit cell is reduced, which makes it possible to achieve increase in capacity.
In a cross-point-type memory cell, a switch device for cell selection is provided other than the memory device. Examples of the switch device may include a switch device configured of metal oxide (for example, see Jiun-Jia Huang et al., 2011 IEEE IEDM11-733˜736 and Wootae Lee et al., 2012 IEEE VLSI Technology symposium p. 37˜38). However, magnitude of a switching threshold voltage of such a switch device is insufficient, and dielectric breakdown may be easily caused upon high voltage application. Other than this, examples of the switch device may include a switch device in which switching is performed at a certain switching threshold voltage and a current is thereby radically increased (Snap Back) (for example, see Myungwoo Son et al., IEEE ELECTRON DEVICE LETTERS, VOL. 32, NO. 11, NOVEMBER 2011, and Seonghyun Kim et al., 2012 VLSI p. 155˜156). In such a switch device, by setting voltage values of selection and non-selection with the switching threshold voltage in between, it is easier to increase a selection current value than in a switch device made of a non-linear resistance material such as metal oxide. It is to be noted that the switching threshold voltage of the above-described switch device may be desirably a voltage that is higher than a write threshold voltage of a memory device to be used in combination. However, the switching threshold voltage of the above-described switch device has not been sufficiently high. Also, when the switch device is used in combination with a storage device having a high write threshold voltage, it is desired to secure a sufficiently-large selection ratio (ON-OFF ratio) between a selected (ON) state and a half-selected (OFF) state in the switch device, which has not been sufficient.
Other than the above-described switch device, for example, a switch device (an ovonic threshold switch (OTS, for example, see Japanese Unexamined Patent Application Publication Nos. 2006-86526 and 2010-157316) using a chalcogenide material, a PN diode, etc. may be mentioned.